f.lux - f. lux is a piece of software for Windows, Mac, Linux, iOS, and Android that provides a blue light filter over your screen. Research suggests limiting our exposure to blue light in the hours before bedtime can help us fall asleep faster.

CareUEyes - CareUEyes is an eye protection software for windows that comes with blue light filter, screen dimmer, and break reminder

Simple Screen Shade - Description and screenshots of Simple Screen Shade.

Dimmer - A very small and free utility for Windows to reduce brightness on LCD/TFT screens.

Nocturne - Nocturne is simple app for switching a computer to night vision mode.

Redshift Color Temperature Adjuster - Redshift adjusts the color temperature according to the position of the sun.